The objective of this proposal is to generate germ cells from two federally approved lines of human embryonic stem cells (hESCs) called UC01 and UC06 (HSF-1 and HSF-6) in order to evaluate the role of transcriptional repression mediated by BLIMP1 and dimethylation of Histone H4 Arginine 3 (H4R3me2) on human germ cell formation. Understanding the molecular regulation of germ cell development is important to improving human health as abnormal germ cells can result in; infertility, which affects 10% of the reproductive age population in the United States, germ cell tumors, which are the most common cancer type to afflict males between the ages of 15 and 35, and birth defects, which occur in children born to parents with abnormal germ line development. In this proposal, we aim to evaluate whether defects in transcriptional repression during the initial stages of germ cell formation in the human fetus result in compromised germ cell development. The role of transcriptional repression will be evaluated in three Specific Aims. Specific Aim 1 involves determining the transcriptional signature of human germ cells from week 6-9 of human fetal gestation. This will be achieved by expression profiling germ cells isolated from human fetal gonads by FACS. Results from this Specific Aim will be used to further clarify the stage of germ cell formation acquired with hESC differentiation, to identify additional cell surface markers that can distinguish hESCs from germ cells, and as a foundation for evaluating the role of transcriptional repressors in germ cell development in vitro. In Specific Aim 2, we will evaluate the effect of a transcriptional repressor, BLIMP1 for a role in regulating human germ cell formation. It is known that BLIMP1 is essential for germ cell formation in murine models. In this Specific Aim, our goal is to knockdown and over express BLIMP1 in hESCs and assay human germ cell formation. This experiment will determine whether the yield of germ cells is reduced in genetically modified verses control ESCs. We will also FACS and isolate human germ cells from differentiating hESCs and evaluate transcription of germ cell specific genes, as well as genes associated with somatic cell differentiation. As a positive control and validation for the use of ESCs to study germ cell formation, we will compare our results to wild type and Blimp1 null mutant murine ESCs for their ability to form germ line in vitro. Finally in Specific Aim 3, the function of PRMT5 and Histone H4R3me2 in human germ cell derivation will be evaluated, and the binding sites of BLIMP1, PRMT5 and dimethylation of Histone H4R3 at promoters in ESCs and germ cells will be identified at a genome-wide level using Chromatin Immunoprecipitation (ChIP) followed by chip. PRMT5 is a protamine arginine methyltransferase that interacts with BLIMP1 to mediate dimethylation of histone H4R3 at loci that need to be repressed in order for germ cell formation to occur. Genes with promoters that share BLIMP1, PRMT5 and Histone H4R3me2 will be analyzed in future proposals. This proposal constitutes the first step from which additional downstream targets essential for normal human germ cell development can be evaluated.